YouTube post says that with monster's mysterious dark hump floating in the water, you'd be forgiven for thinking you'd just spotted the Loch Ness Monster.

The footage shows several fins bobbing up and down in the choppy water, just metres off the coast where children can be seen paddling in the shallow water.

Rebecca Clarke, from London, who filmed the video, said he first believed it was floating garbage, but then realized it was a living creature.

She said: 'It might seem silly but I thought it looked rather reptilian, like a crocodile or a dragon as the fins seemed more rigid than they do on sharks.'

On closer inspection, however, experts say it is likely to be a basking shark lurking near the shoreline of the famous beach resort of Skegness.

Senior biologist Marcus Williams at the National Aquarium in Portsmouth said he could not be certain, but the sighting could have been two basking sharks together.

'It is unusual to see a basking shark for that area of coast, they are, however, typically spotted in the summer months and these we would estimate are larger than five metres.'We have recently seen a second plankton bloom on which the species feed, with water temperatures in excess of 15 degrees Celsius, which are perfect conditions for these gentle giants.